Extending battery life is a key concern for users and manufacturers of cellular telephones and other portable transceivers. A powerful signal generated and transmitted by the wireless transceiver draws more power from the battery than when a lower power signal is generated and transmitted. Accordingly, a number of prior art techniques have been employed to adjust the gain of a portable transmitter so as to not transmit a signal more powerful than necessary for adequate communications. Examples of such ways of automatically adjusting the output power level of a transmitter are described in U.S. Pat. Nos. 4,760,347, 5,129,098, and 5,446,756, incorporated herein by reference.
Although the prior art techniques selectively reduce the output power of the transmitter, the efficiency of the transmitter is not improved by the prior art methods. The transmitter is typically biased, and operating voltages are set, so that the transmitter output signal will not distort in an adverse way at the highest expected output signals. These worse case operating conditions can draw significant power from the battery even when no signal is being transmitted. Such worst case operating conditions are not required when the transmitter is not transmitting its maximum signal. Hence, the transmitter's efficiency is lower when transmitting lower power output signals. A lower efficiency equates to wasting battery power, reducing talk time.
What is needed is a technique for extending the battery life in mobile wireless applications.